1. Field of the Invention
The invention relates to chemical sprayer systems. More particularly, the invention relates to chemical sprayer systems utilizing a hydraulically driven, electronically controlled pumping mechanism.
2. General Background and State of the Art
Commercial chemical sprayer systems are used for applying chemical solutions such as fertilizers and pesticides to a landscape, including, for example, a golf course or an agricultural planting field. Such systems typically are mounted on or incorporated into a vehicle chassis so that the user may efficiently and effectively deliver and distribute the chemical solution over a large amount of real estate.
In this regard, FIG. 1 shows a schematic of a typical prior art sprayer system. It includes a large tank that contains the chemical solution (usually formulated by a mixture of water and concentrated chemical) in fluid communication with a centrifugal pump. Downstream of the pump is a pressure control valve followed by a plurality of electric-solenoid operated on/off valves, each of which is associated with a boom that receives a plurality of nozzles. The booms are typically oriented on a vehicle such that the nozzles on each boom are positioned over the area of ground intended for receipt of the chemical solution. The system also includes lines (both from the pump and from the on/off valves) that direct fluid not otherwise exiting through the nozzles back into the tank.
In operation, a desired amount of chemical solution is manually poured into the tank by the user. Such tanks typically include an agitation pump (not shown) to ensure proper mixing of the chemical solution during this initial filling stage of operation. Once the desired amount of solution is present and mixed in the tank, and once the vehicle has arrived at the desired landscape target, the user will activate the pump. The pump will then draw fluid out of the tank and direct it through the pressure control valve to the on/off valves. Some of the fluid exiting the centrifugal pump is immediately returned to the tank to ensure that the chemical solution in the tank remains substantially homogeneous.
When the user desires to initiate delivery of the chemical solution to the target landscape, the user will activate one or more of the on/off valves so that the fluid is allowed to exit the nozzles situated on the boom (or booms) that have been selected. When the target landscape has been adequately sprayed with the chemical solution or the user, for whatever reason, decides to discontinue or change the fluid delivery scheme, the user will deactivate the appropriate on/off valve(s) and thereby prevent further fluid flow through the associated nozzles. Any pressure spikes that occur due to this change in the state of the on/off valves is mitigated (although not usually eliminated) by the pressure control valve. Finally, to the extent fluid flow to the on/off valve exceeds the amount actually exiting through the associated nozzles, the excess fluid bypasses the nozzles and is directed back into the tank. One example of a spray system that includes many of the concepts described above is the Multi Pro.RTM dedicated spray vehicle previously offered by The Toro Company.
Although prior art sprayer systems such as those described above have generally served to effectively meet the needs of users in the past, there have been lingering desires to improve and advance the way such fluid sprayer systems manage and deliver these fluids. The desire to do so has become more acute in recent times due to heightened sensitivity to environmental issues and to competitive economic pressures. For example, although centrifugal pumps are generally accepted in the industry, centrifugal pumps also have a reputation of needing regular and constant maintenance, particularly as to the integrity of the pump seals. As such, centrifugal pumps present both an economic and environmental challenge to users and purchasers of existing sprayer systems.
On the other hand, alternatives to centrifugal pumps present their own technical challenges. For example, one alternative to a centrifugal pump is a positive displacement pump (e.g., a diaphragm pump), a pump known to offer greater reliability than centrifugal pumps, particularly as to the pump seals. However, the flow and pressure characteristics of positive displacement pumps are such that changes in flow demand in the system create unacceptable conditions for other components of the sprayer system.
For example, when a user decides to activate or deactivate an on/off valve, the resulting change in flow demand leads the positive displacement pump to cause unacceptable pressure spikes in the system. Repeated encounters by the system with such pressure spikes eventually causes deterioration and damage to other parts of the system, including system seals, thus necessitating the very system maintenance and attention that it was hoped could be avoided through the use of such a diaphragm pump. Such pressure spikes can also lead ultimately to inaccurate application of the chemical solution to the target landscape.